When fitting cranes, the individual crane components are usually connected to each other by means of bolts. One very widely-used solution is to hammer substantially cylindrical bolts into the dedicated receptacles in the components to be connected and/or hammer them out again after use. This very simple solution does however necessitate that the corresponding bolt receptacles be very easily reached for hammering, which can no longer always be achieved in ever more complex and compact designs. In order to enable bolting at inaccessible locations or in restricted spaces, bolting systems in which the bolts are hydraulically, pneumatically or mechanically pressed into or withdrawn again from their receptacles have proven to be of value.
Thus, for example, U.S. Pat. No. 8,522,988 B2, US 2004/0104192 A1, U.S. Pat. No. 4,141,455 B1 or DE 200 07 050 U1 show mechanical solutions in which two opposing bolts can be moved away from each other and thus pressed into corresponding bolt receptacles by means of rotating an element which lies between them and comprises a thread, whereas activating the element in reverse can drive the bolts out of their receptacles again. Common to all these solutions is that the central element lying between the bolts comprises two counter-rotating threads which mesh directly with the bolts or indirectly with coupling elements, such that when the element lying between the bolts is rotated, the bolts are moved away from each other or towards each other in a symmetrical movement.
Depending on the size of the bolted arrangement and the type of fit used for it, very large frictional forces may be generated at the points of contact between the bolts and the dedicated receptacles, wherein said forces can be additionally increased by any dirt or soiling. It is also not possible to completely exclude the possibility of the bolts “twisting” up to a certain degree with respect to each other, which additionally increases the forces necessary for moving the bolts.